1. Field of the Invention
This invention relates to an information processing device adapted to be connected to another information processing device typically by way of an IEEE 1394 serial data bus so as to be able to reliably control the subunits it contains. The present invention also relates to an information processing method and a medium that can be used for such a device.
2. Related Background Art
Recently, there have been developed various AV devices that can mutually transmit information typically by way of an IEEE 1394 serial data bus defined by the IEEE (the Institute of Electrical and Electronics Engineers). Then, the devices that are connected to each other by way of such a bus constitute a network system and it is possible to mutually control the AV devices connected to the network by means of predetermined digital interface commands (AV/C command transaction set: to be referred to as AV/C commands hereinafter).
FIG. 1 of the accompanying drawing shows a schematic block diagram of a network formed by using an IEEE 1394 serial data bus 80 (to be referred to simple as bus 80 hereinafter). In a network system as shown in FIG. 1, it is possible to record a video signal received by an IRD (integrated receiver decoder) 71 adapted to receive digital broadcasts by means of a DVCR (digital video cassette recorder) connected to it by way of the bus 80. It is also possible to make recording reservations by using the IRD 71 and the DVCR 81.
When making a recording reservation by using such devices, both the IRD 71 itself and the DVCR 81 are controlled by the controller 72 typically arranged in the IRD 71. More specifically, the recording reservation is made in the IRD 71 (in terms of preselecting the channel, the time of starting the recording and so on). When the selected start time comes, the controller 72 internally so controls the digital tuner subunit 73 in the IRD 71 as to cause it actually select the preselect (reserved) channel and output the video signal and other relates signals received by the digital tuner subunit 73 out of the signals caught by CS antenna 74 to the DVCR 81 by way of the bus 80. At the same time, a recording start command is transmitted from the controller 72 to VCR subunit 84 arranged in the DVCR 81 also by way of the bus 80. Then, the VCR subunit 84 records the video signal transmitted from the digital tuner subunit 73 on a recording medium, which may be a magnetic tape, in response to the recording start command transmitted from the controller 72. In this way, the network of FIG. 1 can record a broadcast according to a recording reservation made for it.
The DVCR 81 is also provided with a controller 82 that controls the operation of recording the video signal received by the analog tuner subunit 83 it contains by mean of a VCR subunit 84.
Electronic devices such as the IRD 71 and the DVCR 81 that are connected to the bus 80 are referred to as units and it is possible to mutually write information to and read any information from any of the units by using a descriptor defined by the general specification of the AV/C command (AV/C command transaction set) (AV/C digital interface command set general specification, which is to be referred to as AV/C general hereinafter). Details of the AV/C general are published and accessible by accessing home page “http://www.1934ta.org/”. Each of the features of a unit is referred to as subunit. In the instance of FIG. 1, there are shown subunits including the digital tuner subunit 73 of the IRD 71 and the VCR subunit 84 if the DVCR 81. There can arise a problem of so-called double booking in a network system as described above in which it is possible to control the operation of the DVCR 81 by some other device connected to it by way of the bus 80 (the IRD 71 in the instance of FIG. 1).
For example, if a recording reservation (recording reservation A) is made for a digital satellite broadcast by way of the IRD 71, the information on the reservation is stored in the controller 72 of the IRD 71. However, since the AV/C command for the recording reservation is not transmitted from the IRD 71 to the DVCR 81 at this time (or at any time before the start of the broadcast for which the recording reservation is made), the DVCR 81 does not known that a recording reservation is made for the broadcast at the IRD 71. If, thereafter, a recording reservation (recording reservation B) is made at the DVCR 81 for an analog terrestrial broadcast that is put on air simultaneously, if partly, with the broadcast of the recording reservation A, the DVCR 81 accept the recording reservation B and stores in it because the controller 82 of the DVCR 81 does not have the information on the recording reservation A made at the IRD 71 and hence does not know that two recording reservations are made for different broadcasts that are put on air simultaneously.
Then, as the time specified by the recording reservation A and the recording reservation B comes, the VCR subunit 84 of the DVCR 81 receives two vide signals, one from the digital tuner subunit 73 of the IRD 71 and one from the analog tuner subunit 83 of the DVCR 81, and is controlled by both the controller 72 of the IRD 71 and the controller 82 of the DVCR 81 to make the VCR subunit 84 of the DVCR 81 at a loss.
Such a problem can occur in a conventional network system having a configuration as described above due to the fact that any of the AV devices (units) connected to the bus 80 cannot obtain detailed information on the recording reservations of all the other AV devices of the system, that each of the AV devices does not have any means for providing the other AV devices of the system with the detailed information on the recording reservations it has, that any of the users of the system cannot know the detailed information on reservations stored in the system when he or she makes a recording reservation and that any of the AV devices or the users cannot input detailed information on a recording reservation.